Self-piercing and clinching fasteners, such as nuts, were developed by a predecessor in interest of the Applicant (Multifastener Corporation) more than 50 years ago as disclosed, for example, in U.S. Pat. No. 2,707,322. Self-piercing and clinching nuts are attached to a metal panel typically in a die press which may also be used to simultaneously form the panel, wherein an installation head is typically attached to the upper die platen of the die press and a die member or die button is attached to the lower die platen of the die press. In the case of a self-piercing nut, a projecting pilot portion pierces an opening in the panel upon closing of the die press and a projecting pilot portion of the pierce nut is then received through the pierced panel opening and clinched to the panel. The same fastener may be utilized as a clinch nut by preforming an opening or prepiercing the panel. The term “self-attaching” fastener is utilized herein as generic to self-piercing and self-clinching fasteners.
More recently, self-attaching male and female fasteners were developed having a tubular barrel portion and a radial flange portion as disclosed, for example, in U.S. Pat. No. 4,555,838 also assigned to the predecessor in interest of the Applicant. The self-attaching fasteners disclosed in this patent include a tubular barrel portion and a radial flange portion that is integral with the tubular barrel portion opposite the free open end of the tubular barrel portion. The self-attaching male fasteners are installed in a die press as described above, wherein the lower die platen typically includes a die button having a panel supporting surface, a central die post, and an annular die cavity surrounding the central die post. The annular die cavity includes a semi-circular annular bottom surface, a radial lip portion at an outer extent of the semi-circular bottom surface, and a generally frustoconical surface extending from the radial lip portion to the end surface of the die button. In certain applications, however, it is preferable to eliminate the outer frustoconical surface and the radial lip portion as disclosed in the above-referenced U.S. patent application Ser. No. 10/714,265.
It is important in most applications of self-attaching fasteners to prevent rotation of the fastener relative to the metal panel in which it is installed. As will be understood, the self-attaching fastener element may be a male fastener having an integral shank portion or a female fastener having a bore and, following attachment of the fastener element to a panel, a second fastener is threaded onto or into the self-attaching fastener element of this invention, typically with a torque wrench. Thus, the self-attaching fastener must be able to withstand the torque applied to the fastener during attachment of a second fastener to the self-attaching fastener. Further, in certain applications, additional torque may be applied to the self-attaching fastener depending upon the application.
Various attempts have been made to improve the torque resistance of self-attaching fasteners of the type disclosed in the above-referenced U.S. Pat. No. 4,555,838. Initially, anti-rotation protrusions or nubs were provided either on the barrel portion or on the radial flange portion adjacent the barrel portion as disclosed, for example, in U.S. Pat. No. 4,810,143, also assigned to the assignee of the predecessor in interest of the assignee of this application. U.S. Pat. No. 5,020,950, also assigned to the predecessor in interest of the assignee of this application, discloses a self-attaching fastener element of the type disclosed herein having a plurality of spaced pockets in the outer edge of the flange portion adjacent the barrel portion. There remains, however, several problems associated with the use of pockets in the flange as disclosed in U.S. Pat. No. 5,020,950, including wear of the die surfaces which form the pockets, such that the pockets are not always fully formed in the flange portion resulting in insufficient torque resistance. Second, the self-attaching fastener and panel assembly is press sensitive. That is, the panel metal may not be fully deformed into the pockets and thus the torque resistance will be inadequate. Further, the pockets form stress risers in the panel which can become a source of failure of the fastener and panel assembly. Finally, the use of pockets in the flange portion may provide insufficient torque resistance, particularly where extreme torque resistance is required.
Further attempts to solve this problem are disclosed in U.S. Pat. No. 5,868,535, also assigned to the predecessor in interest of the assignee of this application. This patent discloses a radial flange portion having a radial surface defining spaced concave surfaces separated by an outer cylindrical surface. During installation of the self-attaching fastener element in the panel, the barrel portion is deformed radially outwardly and upwardly to provide a U-shaped channel that receives the edge of the panel adjacent the opening in the panel. The radial flange portion deforms the panel downwardly into the U-shaped channel, thereby securing the self-attaching fastener element to the panel. The outer cylindrical surfaces further deform the panel providing an interaction between the radial flange portion and the panel which increases the torque resistance of the fastener element in the panel. Although the arcuate design of the radial flange portion disclosed in U.S. Pat. No. 5,868,535 increases the torque resistance and the arcuate configuration is beneficial to deforming the panel due to the smooth transition of its arcuate shape, the torque resistance provided by this self-attaching fastener is still insufficient for certain applications.
Finally, U.S. Pat. No. 5,644,830, also assigned to the predecessor in interest of the assignee of this application, discloses self-attaching fastener elements for forming an electrical connection between the fastener and a metal panel, wherein the disclosed embodiments (FIGS. 15 to 19) include radial projections which bite into the metal panel during installation to form an electrical contact between the fastener and the metal panel. As will be understood, the disclosed embodiments of the radial projections will provide some improvement in torque resistance. However, the configuration of the radial teeth disclosed in this patent will shear the panel under the torque load encountered in many applications. There remains, therefore, a long felt need to provide improved torque resistance for self-attaching fasteners of the type disclosed herein which is provided by the self-attaching fastener element of this invention, particularly self-attaching fastener elements including a tubular barrel portion and a radial flange portion, wherein the tubular barrel portion is deformed to form a mechanical interlock during installation of the fastener element in a metal panel.